关于半波长输电的几个原理性问题

Several Questions of Principles About Half Wavelength Transmission

针对半波长输电中的几个原理性问题展开研究,包括稳态运行时的工频过电压问题、故障引起的工频过电压问题、静态功角同步稳定性问题和暂态功角同步稳定性问题等。文中首先建立了适用于稳态和暂态分析的远距离输电系统等效电路模型,模型中考虑了送端系统和受端系统。为方便描述系统特性,给出了一个采用实际线路参数的测试系统。基于等效电路模型,推导并计算了系统的谐振输电距离。之后,通过理论分析和数值计算寻找系统的可行输电距离范围。结果表明:在考虑暂态频率偏差的情况下,为满足稳态过电压和小干扰稳定性的要求,系统的输电距离应在大于谐振输电距离的一定范围内。当输电距离在上述范围内时,线路中某一特定点的三相短路故障会导致最严重的暂态工频过电压,同时系统很可能失去同步稳定。由于暂态工频过电压和暂态稳定性的约束,半波长输电系统不可能实际运行。

In this paper, several principle questions of half-wavelength transmission are studied, including power frequency overvoltage in steady-state operation, power frequency overvoltage caused by faults, static power angle synchronization stability and transient power angle synchronization stability. The circuit model of the long-distance transmission system is established at first for steady-state and transient analysis. The sending-end system and the receiving-end system are both considered in the model. A test system based on an actual transmission line is given to facilitate the description of system characteristics. Based on the circuit model, the resonant transmission distance of the system is found and calculated. Theoretical analysis and numerical calculations are carried out to determine the feasibility transmission distance. It is demonstrated that the transmission distance should be in a certain range, which is larger than the resonant transmission distance, to satisfy the steady-state overvoltage and the small signal synchronization stability as well as the frequency deviation constraints. For transmission distances in the feasible range, the three-phase short circuit fault at a certain point of the transmission line will cause the most serious transient power-frequency overvoltage, and the system is very likely to lose synchronization stability. Considering the transient power-frequency overvoltage and the transient synchronization stability, the half-wavelength transmission system is technically impossible to operate.